An End Foretold
Like every great comet, C/2012 S1 — better known to the world as Comet ISON — is dying. You could say the story of its demise began 14 months ago, when two observers near Kislovodsk, Russia, stumbled across a dim, fuzzy object while they scanned the sky near the constellations Cancer and Gemini. That fuzz was the outer layers of Comet ISON disintegrating and dispersing as it accelerated toward the warmth of the sun.
You could push further back and trace the comet’s downfall to a fateful event a few million years earlier. At the time, it was an inert chunk of ice, dust and frozen gases, floating nearly motionless in the outermost region of the solar system, a thousand times more distant than Pluto. Then some unknown disturbance, perhaps the nudge of a passing star, dislodged the comet from its stasis and sent it on a self-destructive sunward plunge.
Or you could say that Comet ISON’s end was foretold 4.56 billion years ago, when it and trillions of others like it formed during the birth of the solar system. Some of those comets collided with the infant planets; on Earth, they helped build the atmosphere and fill the oceans. But some of the comets were flung outward into distant cold storage. In that sense, the sunward journey of Comet ISON is a homecoming after a long exile.
Regardless of when the story begins, we know exactly when it will reach its climax: at 1:41 p.m. EST on Nov. 28, 2013, when the ice-packed Comet ISON reaches perihelion — the point closest to the sun — passing less than 750,000 miles (1.2 million kilometers) above the solar surface. There, ISON will roast at more than 2,000 degrees Celsius (hotter than 3,600 degrees Fahrenheit), boiling off layer after layer of its frozen surface. In the process, it will offer a firsthand look at the raw material that Earth and the other planets were built from when the solar system was formed.
